1. Field of the Invention
The present invention relates to a communication system which is comprised by a plurality of base stations and a plurality of terminals, each of the terminals being connected to one of the base stations. More specifically, the invention relates to techniques for connecting base stations wirelessly, without being influenced by a communication between a base station and a terminal, and without influencing it.
2. Description of the Background
As a wireless LAN, a wireless LAN system based on IEEE802.11 (ISO/IEC8802-11:1999(E) ANSI/IEEE Std 802.11, 1999 edition) is known. As one form of such wireless LAN system, an element called a Basic Service Set (BSS) in which a base station covers a plurality of terminals is used, and a plurality of BSSs form a network. A structural element that connects neighboring BSSs is called a Distribution System (DS). A base station establishes (sets) connection to this DS, and packets are transmitted between the BSS and DS via the base station. The entire network extended by the DS is called an ESS (Extended Service Set). In the IEEE802.11 wireless LAN system, a description about implementation of the DS is not specified.
Communications between base stations are also used in a cellular phone system when a terminal connected to a given base station transmits data to a terminal connected to another base station.
The conventional wireless LAN system suffers the following problems.
(1) A practical protocol upon connecting base stations via a wireless communication is not established.
(2) Since a plurality of terminals are connected to a base station, poor reliability of communications between base stations seriously influences the entire system.
(3) Wireless resources are spent for communications between base stations and, in particular, in a system in which base stations and terminals are connected via wireless communications, the communication capacity within the area covered by each base station decreases.